Oxygen flushing pressure die-casting method

ABSTRACT

This disclosure relates to an oxygen flush pressure die-casting method in which the production of shrinkage holes of large caliber appearing within the obtained casting can be prevented and the strength of the product can be remarkably improved by adding to the oxygen gas a minor amount of an inert gas, such as about 1-10 vol percent of the total volume of the mixture.

United States Patent 191 Miki et a].

14 1 July 10,1973

[ OXYGEN FLUSHING PRESSURE DIE-CASTING METHOD [75] Inventors: Isao Miki, Fuji; Yuusuke Ichikawa,

' lhara-gun, both of J apan [73] Assignee: Nippon Light Metal Company Limited, Tokyo, Japan 22 Filed: Aug. 17, 1971 211 App]. No.: 172,579

[30] Foreign Application Priority Data UNITED STATES PATENTS 3,382,910 5/1968 Radtke et al. 164/55 FOREIGN PATENTS OR APPLICATIONS 224,008 11/1968 U.S.S.R 164/55 Primary Examiner-.l. Spencer Overholser Assistant Examiner-John E. Roethel AttorneyWilliam J. Daniel [5 7 ABSTRACT This disclosure relates to an oxygen flush pressure diecasting method in which the production of shrinkage holes of large caliber appearing within the, obtained casting can be prevented and the strength of the product can be remarkably improved'by adding to the oxygen gas a minor amount of an inert gas, such as about 1-10 vol percent of the total volume of the mixture.

6 Claims, No Drawings OXYGEN FLUSHINGPRESSURE DIE-CASTING METHOD This invention relates to an oxygen flush pressure die-casting method and more particularly to an improved oxygen flush pressure die-casting method for obtaining sound die-cast products substantially free of either blow holes or shrinkage holes.

Pressure die-casting is an effective and efficient mass-production casting method for obtaining castings having a beautiful cast surface and high dimensional precision but is subject to the drawback that numerous pores are produced in the castings and reduce their strength.

The main cause for such pores in these die-cast products is the entrapment of air present in the die cavity and injecting sleeve (where injection casting is used) into the melt which appears as numerous blow holes in the products.

As a new casting method to avoid this defect in conventional pressure die-casting, there has been suggested an oxygen flush pressure die-casting method.

According to this improvement, oxygen gas is fed into a die-casting apparatus in advance so that the die cavity and injecting sleeve may be filled with the oxygen gas to replace the air initially present in such spaces and then molten metal is injected'into the die cavity so that the oxygen gas is entrapped into the melt where it reacts with the melt and ultimately appears in the form of fine oxide particles dispersed in the casting. By this method, there can be obtained a casting substantially free of pores produced by the contained gas.

However, on theother hand, castings obtained by the oxygen flush pressure die-casting method exhibit shrinkage pores significantly larger than in castings ob tained by a conventional pressure die-casting method,

a defect which somewhat offsets the initialimportant improvement as is described above.

These shrinkage pores are farlarger. than similar pores produced by contained air-bubbles in conventionally produced castings and are of irregular form, while the pores or blow holes produced'by air bubbles are substantially spherical. Further, whereas the'holes caused by air bubbles are generally distributed over substantially all the parts of the casting, shrinkage pores primarily occur in zones where solidificationof the melt is retarded, such as in the thick parts of the casting, and therefore can be distinctly distinguished from the holes produced by the :air bubbles.

lt has-been found .thatalarge shrinkage pores are more likely to be produced in castings made by anoxygen flush pressure die-castingmethodthanin castings made by conventional pressure die-casting, presumably because, in the latter, the airiis entrapped into :the-meltas numerous compressed air bubbles-dispersedthe melt which, when the melt shrinks during solidification, will expand to some extent to prevent the production of shrinkage pores. On the otherhand, in the oxygen flush pressure 'die-castingmethod, since no 'air bubbles are contained in the melt, the shrinkage of'the melt'by solidification necessarily shows up as :shrinkage :pores :in the part-of the casting where the "solidification occurs latest in point of time.

Although the shrinkage pores produced in castings obtained by such oxygen flush pressure die-casting method are-more visible than the blow'holes resulting from conventional pressure die-casting method, the

total volume of such shrinkage pores in the casting is slight as compared with the total volume of the casting. Hence, it was reasoned thatif in the oxygen flushtechnique, a small amount of inert gas sufficient to compensate by its expansion for theslight volume occupied by the shrinkage pores were to be added to the oxygen gas and this gaseous mixture supplied to the die cavity, the formation of large shrinkagepores could be avoided by the expansion of the contained inert gas during solidification of the melt without offsetting damage to the castings caused bythe development of blow holes from occluded bubbles of the inert gas.

This possibility proved to capable of realization in practice and constitutes the basis of the invention.

An object of the present invention is therefore to provide an oxygen flush pressure die-casting method whereby the formation of large shrinkage pores in the castings is prevented as well as the production of blow holes so that structurally sound die-cast products substantially free of internal defects can be obtained.

In order to further clarify the objects and effects of the present invention, an experimental example made by the present inventor shall be described.

In this experiment, there was used a 300-ton horizontal cold chamber type pressure die-casting apparatus equipped with a device for feeding a gaseous mixture of an oxygen gas and an inert gas at a selected volume ratio continuously into the die casting apparatus through a gas feeding port provided in an injecting sleeve of the apparatus, so that the air in the cavity might be replaced with the gaseous mixture before a melt is injected to produce a die-cast member with the following cross-sectional dimensions; right side thickness 4 mm., central thickness 10 mm., left side thickness 6 mm. and width 150 mm. The melt was of an aluminum allow including 9 percent Si, 3 percent Cu and 0.5 percent Fe, the rest being Al and impurities. This castingwas made by injecting the melt at a casting temperature of 700 C. and amelt injecting'velocity of m/sec. first by a conventional pressure die-casting method wherein no replacement with oxygen gas was made, second, by the oxygen flush method wherein an industrial pure oxygen gas of a purity of 99.9 percent was'introduced into the die-casting apparatus to replace the air present in the die cavity, andthird, by the die-casting method according to the present invention wherein the air in the die cavity was replaced with a gaseousmixture of the same industrial'pure oxygen gas with'sufficiently added nitrogen gas to make 1.5 percentby volume on the total volume. An examination with an 'X-ray permeation testing method was made for internal defects in the cast products obtained in each of these procedures and it-was found that, in the diecast product made by the conventional general pressure die-casting method, numerous blow holes were presentdispersed over the entire product; that, in the die-cast number product made by the oxygen flush pressure-die-casting using only the industrial pure oxy gengas, although no blowholes were present over the entire product, many pores of largecaliber, considered to-be shrinkageporeswere present in the centralthick part of the casting; but that,-in the die-cast member productmade by the method of the present invention wherein the air-was'flushedwith the gaseous mixture to which a small amount of nitrogen had been added, neither large shrinkage-pores nor blow holes were present to a significant extent.

According to many experiments made by the present inventor, it has been found that the amount of inert gas to be added to the oxygen gas introduced into the casting apparatus according to the present invention should be limited to a range of l to percent by volume or preferably about 1 to 5 percent by volume to achieve the shrinkage pore elimination effect without introducing internal defects in the casting substantially due to the formation of gas bubbles in the injected melt. When the amount of added inert gas is less than the above mentioned range, the effect of controlling shrinkage pores produced in the casting will be reduced while, if that range is exceeded, pores from gas bubbles will increase and the soundness of the casting will be impaired.

Inert gases useful for addition to the oxygen gas in the present invention are those which will not react substantially or at all with the metal melt at the casting temperature. According to experiments, it has been found that not only such normally accepted inert gases as nitrogen gas, argon gas or helium gas but also such quasi-inert gases as carbon dioxide or a gaseous mixture of these gases can be used.

In the present invention, in introducing a gaseous mixture of an oxygen gas and an inert gas into a die cavity, the respective gases may be separately fed at a proper volume ratio through gas feeding ports provided in the injecting sleeve or in the casting die of the diecasting apparatus or may be prepared beforehand as a uniform gaseous mixture at a proper volume ratio and fed as such through a gas feeding port. Since a more uniform gaseous mixture can be fed and filled in the die cavity, the latter feeding method has shown a more favorable result.

As described above, by means of the oxygen flushing pressure die-casting improvement of this invention, the

production of voids caused by blow holes and shrinkage pores in the obtained casting can be reduced and the strength of the product thus remarkably improved. Therefore, it is an excellent method for producing diecast products intended to be used as machine parts or as structural members requiring high strength.

We claim:

1. In an oxygen flush pressure die-casting method for injection casting of molten metal into a die cavity wherein air present in said die cavity is displaced in advance with oxygen gas fed into the cavity, the improvement comprising the step of adding a small amount of at least I percent by volume of an inert gas to said oxygen gas which is to displace the air present in said die cavity.

2. An oxygen flush pressure die casting method according to claim 1 wherein said inert gas added to said oxygen gas is selected from the group consisting of carbon dioxide gas, nitrogen gas, argon gas, helium gas and mixtures thereof. 4

3; An oxygen flush pressure die-casting method according to claim 1 wherein the amount of inert gas added to said oxygen gas is inthe range of 1-10 Vol percent of the total gas mixture fed into said die cavity.

4. An oxygen flush pressure die-casting method according to claim 1 wherein said oxygen gas and inert gas are homogeneously mixed exteriorly of the die cavity and then fed into the die cavity through a gas feeding inlet provided in a die casting device.

5. An oxygen flush pressure die-casting method according to claim 1 wherein said oxygen gas and inert gas are fed separately into said die cavity through separate gas feeding inlets provided in a die-casting device.

6. The method of claim 3 wherein the amount of inert gas is l-5 Vol percent of the total gas mixture.

# t i 8 t 

2. An oxygen flush pressure die casting method according to claim 1 wherein said inert gas added to said oxygen gas is selected from the group consisting of carbon dioxide gas, nitrogen gas, argon gas, helium gas and mixtures thereof.
 3. An oxygen flush pressure die casting method according to claim 1 wherein the amount of inert gas added to said oxygen gas is in the range of 1-10 Vol percent of the total gas mixture fed into said die cavity.
 4. An oxygen flush pressure die casting method according to claim 1 wherein said oxygen gas and inert gas are homogeneously mixed exteriorly of the die cavity and then fed into the die cavity through a gas feeding inlet provided in a die casting device.
 5. An oxygen flush pressure die casting method according to claim 1 wherein said oxygen gas and inert gas are fed separately into said die cavity through separate gas feeding inlets provided in a die casting device.
 6. The method of claim 3 wherein the amount of inert gas is 1-5 Vol percent of the total gas mixture. 